Asymmetric battery pack utilizing c-rate balancing

ABSTRACT

The disclosed technology relates to balanced battery packs having battery cells of different capacities with higher capacity battery cells having a reduced impedance compared to lower capacity battery cells in the battery pack. The battery pack includes at least a first and second battery cell connected in parallel, with the second battery cell having a higher capacity than a capacity of the first battery cell. Tabs extending from electrodes of the second battery cell are disposed near a center of the electrodes to reduce an impedance of the second battery cell.

PRIORITY

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Patent Application Ser. No. 62/826,037, entitled “ASYMMETRICBATTERY PACK UTILIZING C-RATE BALANCING,” filed on Mar. 29, 2019, whichis incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to battery cells, and moreparticularly, to asymmetric battery cells in a battery pack that utilizeC-Rate balancing.

BACKGROUND

A jelly roll battery cell includes wound layers of a cathode and ananode, with tabs extending from each to enable electrical connection tothe cathode and anode layers. Conventionally, tabs are located near anend of a cathode and anode layer. Jelly rolls having higher capacitiestypically require longer and/or wider cathode and anode layers comparedto jelly rolls with lower capacities. Connecting two or more jelly rollsin parallel where the jelly rolls have differing capacities, may resultin an imbalance in the charging and/or discharging current supplied toand provided by each jelly roll. In addition, jelly rolls connected inparallel that each have a differing battery cell design (e.g., differingelectrode shape among two or more jelly rolls) but substantially equalcapacities, may nonetheless have an imbalance in the charging and/ordischarging current supplied to and provided by each jelly roll due todifferences in their impedance.

SUMMARY

The disclosed embodiments provide for a battery pack that utilizesC-Rate balancing by reducing an impedance of a higher capacity batterycell to balance a C-Rate of the battery pack. The battery pack includesa first battery cell having a wound set of layers comprising a cathodelayer, an anode layer, and a separator layer disposed between thecathode layer and the anode layer. The first battery cell has a firstcapacity. The battery pack also includes a second battery cell connectedin parallel with the first battery cell. The second battery cellincludes a wound set of layers comprising a cathode layer, an anodelayer, and a separator layer disposed between the cathode layer and theanode layer. The second battery cell has a second capacity that isgreater than the first capacity of the first battery cell, includes afirst cathode tab extending from the cathode layer of the second batterycell, and a first anode tab extending from the anode layer of the secondbattery cell. The first cathode tab is disposed away from a proximal endof the cathode layer of the second battery cell to reduce an impedanceof the second battery cell and balance a C-rate of the second batterycell with a C-rate of the first battery cell.

The disclosed embodiments provide for a battery pack that utilizesC-Rate balancing by reducing an impedance of a higher capacity batterycell to balance a C-Rate of the battery pack. The battery pack includesa first battery cell having a wound set of layers comprising a cathodelayer, an anode layer, and a separator layer disposed between thecathode layer and the anode layer. The first battery cell has a firstcapacity. The battery pack also includes a second battery cell connectedin parallel with the first battery cell. The second battery cellincludes a wound set of layers comprising a cathode layer, an anodelayer, and a separator layer disposed between the cathode layer and theanode layer. The second battery cell has a second capacity that isgreater than the first capacity of the first battery cell, includes afirst cathode tab extending from the cathode layer of the second batterycell, and a first anode tab extending from the anode layer of the secondbattery cell. The first anode tab is disposed away from a proximal endof the anode layer of the second battery cell to reduce an impedance ofthe second battery cell and balance a C-rate of the second battery cellwith a C-rate of the first battery cell.

In some embodiments, a method for balancing a C-rate of battery jellyrolls of different capacities is disclosed. The method includespackaging a first jelly roll having a first capacity and a second jellyroll having a second capacity that is greater than the first capacityinto a battery pack. The method further includes balancing a C-rate ofthe second jelly roll with a C-rate of the first jelly roll bypositioning a first cathode tab and a first anode tab of the secondjelly roll away from a proximal end of a cathode layer and an anodelayer, respectively, to reduce an impedance of the second jelly roll.The method also includes connecting the first jelly roll and the secondjelly roll in parallel.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein may be better understood by referring to thefollowing description in conjunction with the accompanying drawings inwhich like reference numerals indicate identical or functionally similarelements. Understanding that these drawings depict only exemplaryembodiments of the disclosure and are not therefore to be considered tobe limiting of its scope, the principles herein are described andexplained with additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1A illustrates a perspective view of a conventional battery pack;

FIG. 1B illustrates a perspective view of a conventional battery pack;

FIG. 2A illustrates a perspective view of a battery pack, in accordancewith various aspects of the subject technology;

FIG. 2B illustrates a perspective view of a battery pack, in accordancewith various aspects of the subject technology;

FIG. 3A illustrates a cross-section view of a battery cell, inaccordance with various aspects of the subject technology;

FIG. 3B illustrates a cross-section view of a battery cell, inaccordance with various aspects of the subject technology;

FIG. 4A illustrates an unwound battery cell, in accordance with variousaspects of the subject technology;

FIG. 4B illustrates an unwound battery cell, in accordance with variousaspects of the subject technology;

FIG. 4C illustrates an unwound battery cell, in accordance with variousaspects of the subject technology;

FIG. 5A illustrates a cross-section view of a battery cell, inaccordance with various aspects of the subject technology;

FIG. 5B illustrates a cross-section view of a battery cell, inaccordance with various aspects of the subject technology;

FIG. 6A illustrates an unwound battery cell, in accordance with variousaspects of the subject technology;

FIG. 6B illustrates an unwound battery cell, in accordance with variousaspects of the subject technology;

FIG. 7A illustrates a detail view of a tab extending from an electrode,in accordance with various aspects of the subject technology;

FIG. 7B illustrates a detail view of a tab extending from an electrode,in accordance with various aspects of the subject technology;

FIG. 7C illustrates a detail view of a tab extending from an electrode,in accordance with various aspects of the subject technology;

FIG. 8 illustrates a detail view of tabs extending from electrodes, inaccordance with various aspects of the subject technology;

FIG. 9 illustrates a portable electronic device, in accordance withvarious aspects of the subject technology; and

FIG. 10 illustrates an example method for balancing a C-rate of batteryjelly rolls of different capacities, in accordance with various aspectsof the subject technology.

DETAILED DESCRIPTION

Various embodiments of the disclosure are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the disclosure.

A jelly roll battery cell includes wound layers of a cathode and ananode, with tabs extending from each to enable electrical connection tothe cathode and anode layers. Conventionally, tabs are located near anend of a cathode and anode layer. Jelly rolls having higher capacitiestypically require longer and/or wider cathode and anode layers comparedto jelly rolls with lower capacities. Connecting two or more jelly rollsin parallel with each jelly roll having a different capacity, may resultin the higher capacity jelly roll having an increased impedance comparedto the lower capacity jelly roll due to the increased length and/orwidth of an active layer disposed on the electrodes of the highercapacity jelly roll. Further, jelly rolls connected in parallel thateach have a differing battery cell design (e.g., differing electrodeshape among two or more jelly rolls) but substantially equal capacities,may nonetheless have an imbalance in the charging and/or dischargingcurrent supplied to and provided by each jelly roll due to differencesin their impedance. Generally, the longer the electrode length, or widerthe electrode width, the higher the current collector substrateresistance. Jelly rolls having a significant difference in capacityand/or impedance that are connected in parallel, may result in animbalance in the charging and/or discharging current supplied to andprovided by each jelly roll. An imbalance may lead to a lower capacityjelly roll consuming a larger proportion of a charging current.Accordingly, there is a need for certain embodiments of a battery packhaving jelly rolls of different capacities, shapes, and/or designs thathave the same C-Rate to enable the jelly rolls to split the charging anddischarging current in proportion to their respective capacities.

The disclosed technology addresses the foregoing limitations ofconventional asymmetric battery packs by balancing a C-Rate of a highercapacity jelly roll with a C-Rate of a lower capacity jelly roll byrepositioning and/or increasing the number of cathode and anode tabs ofthe higher capacity jelly roll to reduce an impedance of the highercapacity jelly roll to thereby balance a C-Rate of the jelly rolls. Thedisclosed technology further addresses the foregoing limitations ofconventional asymmetric battery packs that comprise battery cellsconnected in parallel that each have a differing battery cell design(e.g., differing electrode shape among two or more battery cells) butsubstantially equal capacities, by reducing an impedance of a higherimpedance battery cell by repositioning and/or increasing the number ofcathode and anode tabs of the higher impedance battery cell to therebybalance a C-Rate of the battery cells. C-Rate balancing allows batterycells connected in parallel to be charged and discharged at the sameC-Rate. In other words, the charging and discharging current is split inproportion to the respective capacity of each connected battery cell.Specifically, because jelly rolls connected in parallel share the samecharge and discharge voltage, a voltage drop of each jelly roll shouldbe made equal, i.e., ΔV=I_(i)Z_(i)=I_(j)Z_(j) where “I” is the load orcurrent in amperes and “Z” is impedance. With C-Rate balancing, thecapacity specific impedance (“QSI”) of each jelly roll should be madeequal, i.e., QSI=Q_(i)Z_(i)=Q_(j)Z_(j), where “Q” is the capacity and“Z” is impedance. The QSI for a particular jelly roll is a function ofelectrode length or width because the longer or wider an electrode, thehigher the substrate resistance.

FIGS. 1A and 1B illustrate perspective views of a conventional batterypack 100. The conventional battery pack 100 includes a firstconventional jelly roll 120 and a second conventional jelly roll 130connected in parallel, enclosed in an enclosure 110. The firstconventional jelly roll 120 may have a lower capacity compared to thesecond conventional jelly roll 130. As a result, the first conventionaljelly roll 120 may be formed of electrodes (e.g., a cathode and an anodelayer) that have a length that is less than a length of electrodes ofthe second conventional jelly roll 130. The first conventional jellyroll 120 may therefore have a smaller width and/or thickness “t”compared to a width and/or thickness “T” of the second conventionaljelly roll 130 based on the number of windings in each of the first andsecond conventional jelly rolls, 120 and 130 respectively. Each of thefirst and second conventional jelly rolls, 120 and 130 respectively, mayhave tabs extending from their respective electrodes disposed at an endof the electrodes of each of the first and second conventional jellyrolls, 120 and 130 respectively. Because the first and secondconventional jelly rolls, 120 and 130 respectively, have differentcapacities and tabs placed at ends of the electrodes, an impedance ofthe second conventional jelly roll 130 is higher than an impedance ofthe first conventional jelly roll 120. As a result, a disproportionateamount of charging current may be directed to the first conventionaljelly roll 120 having a lower impedance and a lower capacity which maylead to poor battery pack 100 performance with respect to chargingand/or discharging.

As shown in FIG. 1A, the first and second conventional jelly rolls, 120and 130 respectively, may be arranged in a side-by-side configuration.Tabs extend from ends of the electrodes of the first and secondconventional jelly rolls, 120 and 130 respectively. When wound, the tabsare positioned at the center of each of the first and secondconventional jelly rolls, 120 and 130 respectively. Referring to FIG.1B, the first and second conventional jelly rolls, 120 and 130respectively, may be arranged in a stacked configuration.

FIGS. 2A and 2B illustrate perspective views of a battery pack 200, inaccordance with various aspects of the subject technology. The batterypack 200 may comprise a first battery cell 220 and a second battery cell230 connected in parallel, and enclosed in an enclosure 210. The firstbattery cell 220 may have a first capacity and the second battery cell230 may have a second capacity that is greater than the first capacityof the first battery cell 220. As shown in FIG. 2A, the first and secondbattery cells, 220 and 230 respectively, may be arranged in aside-by-side configuration. As shown in FIG. 2B, the first and secondbattery cells, 220 and 230 respectively, may be arranged in a stackedconfiguration. Other arrangements and battery pack 200 configurationsare contemplated without departing from the scope of the subjecttechnology.

It is also understood that the battery pack 200 may comprise a firstbattery cell 220 and a second battery cell 230 connected in parallel,each having the same capacity. The second battery cell 230, however, mayhave a higher impedance than the first battery cell 220 based on adifferent battery cell design for the second battery cell 230. Forexample, the second battery cell 230 may have a length that is 2X longerthan a length of the first battery cell 220, and the second battery cell230 may have a width that is ½ narrower than a width of the firstbattery cell 220. Each of the first and second battery cells, 220 and230 respectively, may therefore, have a substantially equal surface area(A=L*W) and thus, have a substantially equal capacity, but with animpedance imbalance. In this example, because the second battery cell230 has a length that substantially greater than the length of the firstbattery cell 220, the impedance of the second battery cell 230 isgreater than the impedance of the first battery cell 220.

FIG. 3A illustrates a cross-section view of the first battery cell 220,in accordance with various aspects of the subject technology. The firstbattery cell 220 may comprise a wound set of layers comprising a cathodelayer 310A, an anode layer 320A, a first separator layer 330A disposedbetween the cathode layer 310A and the anode layer 320A, and a secondseparator layer 340A disposed between the anode layer 320A and thecathode layer 310A. Proximate to or at a first end 350A of the cathodelayer 310A and the anode layer 320A of the first battery cell 220, afirst cathode tab 315A may extend from the cathode layer 310A, and afirst anode tab 325A may extend from the anode layer 320A.

FIG. 3B illustrates a cross-section view of the second battery cell 230,in accordance with various aspects of the subject technology. The secondbattery cell 230 may comprise a wound set of layers comprising a cathodelayer 310B, an anode layer 320B, a first separator layer 330B disposedbetween the cathode layer 310B and the anode layer 320B, and a secondseparator layer 340B disposed between the anode layer 320B and thecathode layer 310B.

The cathode layer 310A,B may be an aluminum foil coated with a lithiumcompound (e.g., LiCoO₂) and the anode layer 320A,B may be a copper foilcoated with carbon or graphite. The separator 330A,B and 340A,B mayinclude polyethylene (PE), polypropylene (PP), and/or a combination ofPE and PP, such as PE/PP or PP/PE/PP. The wound set of layers areenclosed within enclosure 210 and immersed in an electrolyte, which forexample, can be a LiPF6-based electrolyte that can include EthyleneCarbonate (EC), Polypropylene Carbonate (PC), Ethyl Methyl Carbonate(EMC) or DiMethyl Carbonate (DMC). The electrolyte can also includeadditives such as Vinyl carbonate (VC) or Polyethylene Soltone (PS). Theelectrolyte can additionally be in the form of a solution or a gel.

The second battery cell 230 further comprises a first cathode tab 315Bextending from the cathode layer 310B, and a first anode tab 325Bextending from the anode layer 320B. In one aspect, the first cathodetab 315B is disposed away from a first end 350B of the cathode layer310B of the second battery cell 230 to reduce an impedance of the secondbattery cell 230 and balance a C-rate of the second battery cell 230with a C-rate of the first battery cell 220. In another aspect, thefirst anode tab 325B is disposed away from the first end 350B of theanode layer 320B of the second battery cell 230 to reduce the impedanceof the second battery cell 230 and balance the C-rate of the secondbattery cell 230 with the C-rate of the first battery cell 220.

FIG. 4A illustrates an unwound first battery cell 220, in accordancewith various aspects of the subject technology. The unwound firstbattery cell 220 comprises the cathode layer 310A and the anode layer320A. The cathode layer 310A has a first length 405 defined by adistance between the first end 350A and a second end 360A of the cathodelayer 310A. The anode layer 320A has a length defined by a distancebetween the first end 350A and the second end 360A of the anode layer320A that may be about the first length 405.

The cathode tab 315A extending from the cathode layer 310A may bedisposed a distance 415 from the first end 350A of the cathode layer310A. The anode tab 325A may be disposed a distance 425 from the firstend 350A of the anode layer 320A. In one aspect, the cathode tab 315Aand the anode tab 325A are disposed at or near the first end 350A.

FIG. 4B illustrates an unwound second battery cell 230, in accordancewith various aspects of the subject technology. The unwound secondbattery cell 230 comprises the cathode layer 310B and the anode layer320B. The cathode layer 310B has a second length 455 defined by adistance between the first end 350B and a second end 360B of the cathodelayer 310B that is greater than the first length 405 of the firstbattery cell 220. The anode layer 320B has a length defined by adistance between the first end 350B and the second end 360B of the anodelayer 320B that may be about the second length 455.

In one aspect, because the length 405 of the electrodes (e.g., cathodelayer 310A and anode layer 320A) of the first battery cell 220 is lessthan the length 455 of the electrodes (e.g., cathode layer 310B andanode layer 320B) of the second battery cell 230, the capacity of thefirst battery cell 220 is less than the capacity of the second batterycell 230. In another aspect, because the length 455 of the secondbattery cell 230 is greater than the length 405 of the first batterycell 220, placement of the cathode tab 315B extending from the cathodelayer 310B and/or placement of the anode tab 325B extending from theanode layer 320B may be disposed away from the first end 350B of thecathode layer 310B and anode layer 320B, respectively, to reduce animpedance of the second battery cell 230 and to balance the C-rate ofthe second battery cell 230 with the C-rate of the first battery cell220.

For example, as shown in FIG. 4B, the cathode tab 315B may be disposedproximate to a midpoint of the length 455 of the cathode layer 310B at adistance 465. The anode tab 325B may be similarly disposed proximate tothe midpoint of the length 455 of the anode layer 320B at a distance475. Alternatively, the cathode tab 315B and/or the anode tab 325B maybe disposed proximate to one-third or two-thirds of the length 455 ofthe cathode layer 310B and/or the anode layer 320B, respectively. Bypositioning the cathode tab 315B and/or the anode tab 325B at or nearthe midpoint, one-third, or two-thirds of the length of the electrodes,the impedance of the second battery cell 230 may be reduced, therebysplitting a charging or discharging current in proportion to therespective capacities of the first battery cell 220 and the secondbattery cell 230. For example, the first battery cell 220 may have acapacity of 1,000 mAh and an impedance of 200 milli-ohms, and the secondbattery cell 230 may have a capacity of 2,000 mAh and an impedance of100 milli-ohms, despite having a length 455 that is much larger than alength 405 of the first battery cell 220. By positioning the cathode tab315B and the anode tab 325B at or near the midpoint, one-third, ortwo-thirds of the length of the electrodes (e.g., cathode layer 310B andanode layer 320B) of the second battery cell 230, the impedance of thesecond battery cell 230 may be reduced compared to an impedance ofconventional battery cells (e.g., conventional jelly rolls 120, 130)having tabs disposed at or near an end of the electrodes.

FIG. 4C illustrates an alternative embodiment of the unwound batterycell 230, in accordance with various aspects of the subject technology.In one aspect, the cathode layer 310B may have more than one cathode tab315B extending therefrom, and the anode layer 320B may have more thanone anode tab 325B extending therefrom. Specifically, because the length455 of the second battery cell 230 is greater than the length 405 of thefirst battery cell 220, increasing the number of cathode tabs 315Band/or increasing the number of anode tabs 325B may reduce an impedanceof the second battery cell 230 to balance the C-rate of the secondbattery cell 230 with the C-rate of the first battery cell 220.

For example, as shown in FIG. 4C, a first cathode tab 315B may bedisposed proximate to the first end 350B of the cathode layer 310B and asecond cathode tab 315B may be disposed proximate to the second end360B. A first anode tab 325B may be similarly disposed proximate to thefirst end 350B of the anode layer 320B and a second anode tab 325B maybe disposed proximate to the second end 360B. By increasing the numberof cathode tabs 315B and/or the anode tabs 325B, the impedance of thesecond battery cell 230 may be reduced (compared to an impedance ofconventional jelly rolls 120, 130), thereby splitting a charging ordischarging current in proportion to the respective capacities of thefirst battery cell 220 and the second battery cell 230

FIG. 5A illustrates a cross-section view of the first battery cell 220,in accordance with various aspects of the subject technology. Asdescribed above, the first battery cell 220 may comprise the wound setof layers comprising the cathode layer 310A, the anode layer 320A, thefirst separator layer 330A disposed between the cathode layer 310A andthe anode layer 320A, and the second separator layer 340A disposedbetween the anode layer 320A and the cathode layer 310A. Proximate to orat the first end 350A of the cathode layer 310A and the anode layer 320Aof the first battery cell 220, the first cathode tab 315A may extendfrom the cathode layer 310A, and the first anode tab 325A may extendfrom the anode layer 320A.

FIG. 5B illustrates a cross-section view of an alternative secondbattery cell 230, in accordance with various aspects of the subjecttechnology. The second battery cell 230 may comprise the wound set oflayers comprising the cathode layer 310B, the anode layer 320B, thefirst separator layer 330B disposed between the cathode layer 310B andthe anode layer 320B, and the second separator layer 340B disposedbetween the anode layer 320B and the cathode layer 310B. The secondbattery cell 230 further comprise a plurality of cathode tabs 515A-Nextending from the cathode layer 310B, and a plurality of anode tabs525A-N extending from the anode layer 320B. In one aspect, the pluralityof cathode tabs 515A-N may be equally spaced apart along a length of thecathode layer 310B of the second battery cell 230, may be positioned onevery wrap, every second wrap, every third wrap, or every fourth wrap;to reduce an impedance of the second battery cell 230 and balance aC-rate of the second battery cell 230 with a C-rate of the first batterycell 220. In another aspect, the plurality of anode tabs 525A-N may beequally spaced apart along a length of the anode layer 320B, may bepositioned on every wrap, every second wrap, every third wrap, or everyfourth wrap; to reduce the impedance of the second battery cell 230 andbalance the C-rate of the second battery cell 230 with the C-rate of thefirst battery cell 220.

FIG. 6A illustrates an unwound first battery cell 220, in accordancewith various aspects of the subject technology. As described above, theunwound first battery cell 220 comprises the cathode layer 310A and theanode layer 320A. The cathode layer 310A has the first length 405 andthe anode layer 320A has a length that may be about the first length405. The cathode tab 315A extending from the cathode layer 310A may bedisposed the distance 415 from the first end 350A of the cathode layer310A. The anode tab 325A may be disposed the distance 425 from the firstend 350A of the anode layer 320A. In one aspect, the cathode tab 315Aand the anode tab 325A are disposed at or near the first end 350A.

FIG. 6B illustrates an alternative unwound second battery cell 230, inaccordance with various aspects of the subject technology. The unwoundsecond battery cell 230 comprises the cathode layer 310B and the anodelayer 320B. The cathode layer 310B has a third length 505 defined by adistance between the first end 350B and a second end 360B of the cathodelayer 310B that is greater than the first length 405 of the firstbattery cell 220. The anode layer 320B has a length defined by adistance between the first end 350B and the second end 360B of the anodelayer 320B that may be about the third length 505.

In one aspect, because the length 405 of the electrodes (e.g., cathodelayer 310A and anode layer 320A) of the first battery cell 220 is lessthan the length 505 of the electrodes (e.g., cathode layer 310B andanode layer 320B) of the second battery cell 230, the capacity of thefirst battery cell 220 is less than the capacity of the second batterycell 230. In another aspect, because the length 505 of the secondbattery cell 230 is greater than the length 405 of the first batterycell 220, utilizing the plurality of cathode tabs 315B that each extendfrom the cathode layer 310B and/or the plurality of anode tabs 325B thateach extend from the anode layer 320B reduces an impedance of the secondbattery cell 230 and balances the C-rate of the second battery cell 230with the C-rate of the first battery cell 220.

For example, as shown in FIG. 6B, the cathode layer 310B may comprise aplurality of cathode tabs 515A-D that are spaced apart at increasingintervals with respect to the length 505 of the cathode layer 310B ofthe second battery cell 230. For example, a first cathode tab 515A and asecond cathode tab 515B may be spaced apart by a distance 535. Thesecond cathode tab 515B and a third cathode tab 515C may be spaced apartby a distance 545, that is more than the distance 535. The third cathodetab 515C and a fourth cathode tab 515D may be spaced apart by a distance555, that is more than the distance 545.

The anode layer 320B may comprise a plurality of anode tabs 525A-D thatare spaced apart at increasing intervals with respect to the length 505of the anode layer 320B of the second battery cell 230. For example, afirst anode tab 525A and a second anode tab 525B may be spaced apart bya distance 565. The second anode tab 525B and a third anode tab 525C maybe spaced apart by a distance 575, that is more than the distance 565.The third anode tab 525C and a fourth anode tab 525D may be spaced apartby a distance 585, that is more than the distance 575.

By utilizing the plurality of cathode tabs 515A-N and/or the pluralityof anode tabs 525A-N, the impedance of the second battery cell 230 maybe reduced, thereby splitting a charging or discharging current inproportion to the respective capacities of the first battery cell 220and the second battery cell 230. For example, the first battery cell 220may have a capacity of 1,000 mAh and an impedance of 200 milli-ohms, andthe second battery cell 230 may have a capacity of 2,000 mAh and animpedance of 100 milli-ohms despite having a length 505 that is muchlarger than a length 405 of the first battery cell 220. By utilizing theplurality of cathode tabs 515A-N and/or the plurality of anode tabs525A-N, the impedance of the second battery cell 230 may be reducedcompared to an impedance of conventional battery cells (e.g.,conventional jelly rolls 120, 130) having a single tab disposed at ornear an end of the electrodes.

It is also understood that while the plurality of cathode tabs 515A-Nand the plurality of anode tabs 525A-N are discussed herein withreference to the second battery cell 230, the first battery cell 220 mayalso utilize the tab positioning described herein to reduce an impedanceof the first battery cell 220, if desired. The battery pack 200, maytherefore utilize battery cells 220, 230 that each implement animpedance reduction scheme, as described above.

FIGS. 7A-7C illustrate detail views of a tab 315B, 325B extending froman electrode, in accordance with various aspects of the subjecttechnology. The tab 315B may extend from the cathode layer 310B and/orthe tab 325B may extend from the anode layer 320B. As shown in FIG. 7A,the tab 315B, 325B may extend from an outer edge of the cathode layer310B and anode layer 320B, respectively. Referring to FIG. 7B, the tab315B, 325B may extend toward a centerline of the cathode layer 310B andanode layer 320B, respectively. In some aspects, by extending the tab315B, 325B toward the centerline of the cathode layer 310B and/or anodelayer 320B, a surface area of the tab 315B, 325B in contact with thecathode layer 310B and/or anode layer 320B is increased to furtherreduce an impedance of the second battery cell 230. Referring to FIG.7C, the tab 315B, 325B may extend along an entire width of the cathodelayer 310B and anode layer 320B, respectively. In some aspects, byextending along the entire width of the cathode layer 310B and/or anodelayer 320B, a surface area of the tab 315B, 325B in contact with thecathode layer 310B and/or anode layer 320B is further increased tofurther reduce an impedance of the second battery cell 230.

FIG. 8 illustrates a detail view of tabs 315B, 325B extending fromelectrodes, in accordance with various aspects of the subjecttechnology. In one aspect, the cathode tab 315B of the second batterycell 230 may extend from a first edge of the cathode layer 310B. Theanode tab 325B of the second battery cell 230 may extend from a secondedge, opposite the first edge, of the anode layer 320B.

FIG. 9 illustrates a portable electronic device 900, in accordance withvarious aspects of the subject technology. The above-describedrechargeable battery pack 200 can generally be used in any type ofelectronic device. For example, FIG. 9 illustrates a portable electronicdevice 900 which includes a processor 902, a memory 904 and a display906, which are all powered by the battery pack 200. Portable electronicdevice 900 may correspond to a laptop computer, tablet computer, mobilephone, personal digital assistant (PDA), digital music player, watch,and wearable device, and/or other type of battery-powered electronicdevice. Battery pack 200 may correspond to a battery pack that includesone or more battery cells 220, 230. Each battery cell 220, 230 mayinclude a set of layers, including a cathode with an active coating, aseparator, an anode with an active coating, with the battery pack 200utilizing C-Rate balancing as described above.

FIG. 10 illustrates an example method 1000 for balancing a C-rate ofbattery jelly rolls of different capacities, in accordance with variousaspects of the subject technology. It should be understood that, for anyprocess discussed herein, there can be additional, fewer, or alternativesteps performed in similar or alternative orders, or in parallel, withinthe scope of the various embodiments unless otherwise stated.

At operation 1010, a first jelly roll having a first capacity and asecond jelly roll having a second capacity that is greater than thefirst capacity are packaged into a battery pack. The first and secondjelly rolls each comprise a cathode layer, an anode layer, and aseparator layer disposed between the cathode layer and the anode layer.At operation 1020, a C-rate of the second jelly roll is balanced with aC-rate of the first jelly roll by positioning a first cathode tab and afirst anode tab of the second jelly roll away from a proximal end of acathode layer and an anode layer, respectively, to reduce an impedanceof the second jelly roll. At operation 1030, the first jelly roll andthe second jelly roll are connected in parallel.

In another aspect, an example method for balancing a C-rate of jellyrolls of different impedances may include packaging a first jelly rollhaving a first impedance and a second jelly roll having a secondimpedance that is greater than the first impedance into a battery pack.The first and second jelly rolls each comprise a cathode layer, an anodelayer, and a separator layer disposed between the cathode layer and theanode layer. A C-rate of the second jelly roll is balanced with a C-rateof the first jelly roll by positioning a first cathode tab and a firstanode tab of the second jelly roll away from a proximal end of a cathodelayer and an anode layer, respectively, to reduce an impedance of thesecond jelly roll.

Although a variety of examples and other information was used to explainaspects within the scope of the appended claims, no limitation of theclaims should be implied based on particular features or arrangements insuch examples, as one of ordinary skill would be able to use theseexamples to derive a wide variety of implementations. Further andalthough some subject matter may have been described in languagespecific to examples of structural features and/or method steps, it isto be understood that the subject matter defined in the appended claimsis not necessarily limited to these described features or acts. Forexample, such functionality can be distributed differently or performedin components other than those identified herein. Rather, the describedfeatures and steps are disclosed as examples of components of systemsand methods within the scope of the appended claims.

1-11. (canceled)
 12. A battery pack, comprising: a first battery cell,the first battery cell comprising a wound set of layers comprising acathode layer, an anode layer, and a separator layer disposed betweenthe cathode layer and the anode layer, wherein the first battery cellhas a first capacity a second battery cell connected in parallel withthe first battery cell, the second battery cell comprising a wound setof layers comprising a cathode layer, an anode layer, and a separatorlayer disposed between the cathode layer and the anode layer, whereinthe second battery cell has a second capacity that is greater than thefirst capacity of the first battery cell; wherein the second batterycell further comprises a first cathode tab extending from the cathodelayer of the second battery cell, and a first anode tab extending fromthe anode layer of the second battery cell; and wherein the first anodetab is disposed away from a proximal end of the anode layer of thesecond battery cell to reduce an impedance of the second battery celland balance a C-rate of the second battery cell with a C-rate of thefirst battery cell.
 13. The battery pack of claim 12, wherein the anodelayer of the second battery cell has a length; and wherein the firstanode tab of the second battery cell is disposed proximate to a midpointof the length of the anode layer of the second battery cell.
 14. Thebattery pack of claim 12, further comprising a second anode tabextending from the anode layer of the second battery cell, wherein thefirst anode tab of the second battery cell is disposed at a distal endof the anode layer of the second battery cell and the second anode tabof the second battery cell is disposed at the proximal end of the anodelayer of the second battery cell.
 15. The battery pack of claim 12,further comprising a second anode tab and a third anode tab extendingfrom the anode layer of the second battery cell, wherein the first anodetab, the second anode tab, and the third anode tab of the second batterycell are spaced apart at increasing intervals with respect to a lengthof the anode layer of the second battery cell.
 16. A method forbalancing a C-rate of battery jelly rolls of different capacities, themethod comprising: packaging a first jelly roll having a first capacityand a second jelly roll having a second capacity that is greater thanthe first capacity into a battery pack; balancing a C-rate of the secondjelly roll with a C-rate of the first jelly roll by positioning a firstcathode tab and a first anode tab of the second jelly roll away from aproximal end of a cathode layer and an anode layer, respectively, toreduce an impedance of the second jelly roll; and connecting the firstjelly roll and the second jelly roll in parallel.
 17. The method ofclaim 16, wherein the cathode layer has a length; and wherein the firstcathode tab is disposed proximate to a midpoint of the length of thecathode layer.
 18. The method of claim 17, wherein the anode layer has alength; and wherein the first anode tab is disposed proximate to amidpoint of the length of the anode layer.
 19. The method of claim 16,wherein the cathode layer has a length; wherein the second jelly rollfurther comprises a second cathode tab and a third cathode tab; andwherein the first cathode tab, the second cathode tab, and the thirdcathode tab are spaced apart at increasing intervals with respect to thelength of the cathode layer.
 20. The method of claim 19, wherein theanode layer has a length; wherein the second jelly roll furthercomprises a second anode tab and a third anode tab; and wherein thefirst anode tab, the second anode tab, and the third anode tab arespaced apart at increasing intervals with respect to the length of theanode layer.